Lecture 4

Question 1

What kind of fluid is blood plasma

Answer 1

considered newtonian at low protein concentration

Question 2

What are 3 key observations relating to blood viscosity

Answer 2

Viscosity increases with increasing hematocrit
Viscosity decreases with increasing shear rate
Viscosity decreases with decreasing radius of conduit

Question 3

Explain the 4 non-newtonian models

Answer 3

Power law
Bingham
Casson
Herschel-Bulkley

Question 4

Explain fahraeus linqvist effect

Answer 4

The ratio of tube hematocrit/discharge hematocrit decreases with decreasing tube diameter until the diameter reaches the size of a RBC

Question 5

Whats hematocrit

Answer 5

RBC concentration in blood

Question 6

Whats Qv

Answer 6

Volumetric flow Qv (m^3/s) is the volume of fluid that passes through a given surface or area per unit of time

Qv = vavg*Ac

Question 7

Components of blood

Answer 7

Components
– Plasma
– Platelets (thrombocytes)
– White blood cells (leukocytes) – Red blood cells (erythrocytes) – Other proteins

Question 8

Hematocrit

Answer 8

Hematocrit, H
– Volume percentage of red blood cells
– H=40-50%

Question 9

What can we say about blood plasma

Answer 9

It increases with protein concentration

We consider it to behave newtonian

Question 10

Whats relative apparent viscosity

Answer 10

eta r (relative apparent viscosity) =
aparrent viscosity eta / µp (plasma viscosity)

This gives us a ratio of how much more blood is viscous compared to pure plasma (effect of RBCs)

At a relative viscosity of 1, there is no effect of RBCs
At a higher relative viscosity, red blood cells increase the viscosity compared to plasma alone

Question 11

Explain this phenomenon: Viscosity of blood increases with increasing hematocrit

Answer 11

More hematocrit means more RBCs in the blood, which increases the viscosity because there are more particles interacting and resisting flow.

However, because normal RBCs are flexible and deform under shear stress, they can flow more easily than if they were rigid (like sickle cells), reducing the overall increase in viscosity.

Question 12

Explain this phenomenon: Viscosity decreases with decreasing radius of conduit

Answer 12

Fahraeus-Lindqvist effect:

Feed hematocrit = Discharge hematocrit, since the total number of RBCs remains the same.

Tube hematocrit is lower because the RBCs travel faster through the tube than the surrounding plasma.

As the tube gets narrower, the difference between tube hematocrit and discharge hematocrit increases, leading to a lower ratio Ht/Hd

Question 13

Explain this phenomenon: Viscosity decreases with increasing shear rate

Answer 13

At lower shear rates: Red blood cells (RBCs) tend to aggregate and form structures called rouleaux (stacks of RBCs), which increase the apparent viscosity. This is because the larger aggregates encounter more resistance as they flow, making the blood more viscous.

At higher shear rates: The increased flow causes RBCs to deform and elongate, which reduces their effective size and allows them to flow more easily. This deformation decreases the apparent viscosity, as the cells can pass by each other more smoothly, thus reducing resistance.

Sickle cells have less shear thinning ability